MORPHOLOGY 
extensive that usually only one mother cell functions, all the others 
contributing to its nutrition (fig. 302). This results in a relatively very 
FIGS. 298-300. Sporangium of Selaginella: 298, section through tip of strobilus, 
showing young sporangium (two shaded cells) on stem, and below it a young sporo- 
phyll; 299, further development of sporangium; the superficial cell of the sporophyll 
containing a nucleus is to give rise to the ligule; 300, sporangium in the mother cell 
stage. 298 and 299, after Miss LYOX. 
large mother cell and a tetrad of four very large spores. In some 
cases, although a tetrad of spores is started, two or three of them may 
not develop further, resulting in a sporangium containing only one or 
two spores. It is this 
condition of dissimilar 
spores that is called 
helerospory, in con- 
trast with the condi- 
tion of similar spores 
(as in Lyco podium), 
which is called homo- 
spory. Selaginella, 
therefore, is hetero- 
s porous, while Lycopo- 
dium is homosporous. 
FIGS. 301, 302. Sporangia of Selaginella: 301, micro- The terminology 
sporangium, showing all the mother cells forming tetrads; applied to the hetero- 
302, megasporangium, showing one functioning mother cell ... 
(shaded), the other mother cells acting as nutritive cells. sporous Condition IS 
After Miss LYON. simple. The small 
